1. Field of Invention
The present invention relates to a projector for projecting and displaying an image. More specifically, it relates to a projector using a DMD(trademark).
2. Description of Related Art
A projector which modulates a light beam irradiated by a light source using an electric optical device and projects the modulated light beam onto a screen in an enlarged manner using a projection lens has been known.
As an optical modulator constituting the electric optical device, DMD (digital Micro-mirror Device: registered Trademark of Texas Instruments Incorporated, hereinafter referred to as DMD) as a reflective optical modulator for modulating a light beam irradiated by a light source in accordance with image information by controlling incident angle of micro-mirrors is known.
The DMD modulates a light beam from a light source in accordance with image data and irradiates modulated light as an image light representing an image, of which two-dimensionally arrayed pixels are constructed of minute mirrors, the inclination of the mirrors being controlled by a function of electrostatic field of memory element disposed directly below each pixel, so that the reflection angle of the reflected light is changed to set on/off condition and the light reflected in a predetermined direction is incident on a projection lens to be projected as an image light.
When the pixel is in off condition, the light beam reflected by DMD is not incident on the projection lens and is not projected as an image signal, which is introduced to a predetermined location in the electric optical device.
According to such arrangement, the light beam from the light source can be deflected by switching on and off conditions, thereby conducting optical switching with superior S/N ratio.
However, according to the above arrangement, the light beam reflected by the DMD when the pixel is off, i.e. the light beam not introduced to the projection lens, is introduced to a predetermined location in the device, which is disposed of as redundant light among all the light beam irradiated by the light source. The existence of redundant light greatly reduces the total light amount of the image projected through the projection lens relative to the total light amount directly irradiated by the light source, thereby reducing peak luminance of the displayed image.
Further, when the pixel is off, since the light reflected by DMD is not incident on the projection lens as an image light and is introduced to a predetermined location in the device, the introduced light is reflected inside the device and is taken into the projection lens as a stray light, so that the contrast ratio of the image projected on the screen is lowered.
An object of the present invention is to provide a projector capable of improving peak luminance of image light and achieving high contrast ratio.
A projector according to an aspect of the present invention has: a light source; a reflective optical modulator that modulates a light beam irradiated by the light source in accordance with image information by controlling an incident angle of a micro-mirror, the modulated light beam being enlarged and projected by a projection optical system; and a light-composite path that combines the light beam modulated by the reflective optical modulator and not incident on the projection optical system with the light beam irradiated by the light source, the combined light beam being introduced again onto the reflective optical modulator.
According to the above aspect of the present invention, since the light-composite path for getting the light beam irradiated by the reflective optical modulator and not incident on the projection optical system to be again incident on the reflective optical modulator is provided, the light beam not incident on the projection optical system, i.e. the redundant light, can be supplied on the reflective optical modulator by the light-composite path, so that, when white area is displayed on non-display (black display) area of a projection image for instance, the luminance of the white area can be enhanced and contrast between white and black areas can be increased.
Further, since total light amount incident on the micro-mirror can be increased even when the size of the micro-mirror of the optical modulator is reduced, i.e. when the size of the picture element is reduced sufficient peak luminance and high contrast ratio can be attained.
Since the total light amount incident on the micro-mirror can be increased, the light amount of the projection image can be increased. Accordingly, the distance between the projection screen and the projection optical system can be sufficiently widened and an image of sufficiently high contrast ratio can be viewed even when the projection image is enlarged to correspond to large-screen.
Further, since the light-composite path is provided, the light beam irradiated by the optical modulator and not incident on the projection optical system can be prevented from being reflected on the components in the device to be taken into the projection optical system when the light beam is introduced to a predetermined location in the device, the deterioration of the contrast ratio of the projection image on account of stray light can be prevented and stable projection image can be maintained.
In the present invention, a second optical modulator may preferably be provided in the light-composite path, the second optical modulator switching introduction and block of the flow of the light beam not incident on the projection optical system toward the reflective optical modulator in synchronization with the image information.
The second optical modulator may be liquid crystal shutter and a reflective optical element capable of adjusting attitude thereof in the light-composite path.
When the projection image is set to non-displayed (black display) condition, the light beam irradiated by the light source enters into the light-composite path via the reflective optical modulator and the light passing through the light-composite path is again incident on the reflective modulator. By repeating such cycles, the light amount of the light beam incident on the reflective optical modulator increases and the light amount of the non-display image can be increased.
Since the second optical modulator is provided in the light-composite path, the light beam incident on the reflective optical modulator can be blocked by the second optical modulator, thus preventing increase in the light amount of the non-display image.
In the present invention, an optical integrator that equalizes the illuminance distribution of the light beam not incident on the projection optical system before introducing on the reflective optical modulator may preferably be provided in the light-composite path.
The beam splitter used for the optical integrator may be a multi-lens array using avertically and horizontally aligned lenses and a rod integrator using multiple reflections by inside total-reflection.
When the light beam irradiated by the light source is reflected by the reflective optical modulator, the image light incident on the projection optical system to be irradiated as an image and the light beam entering into the light-composite path are reversed. When the light beam passes through the light-composite path and is incident again on the reflective optical modulator, the light amount of the image light does not increase if the light beam is reversed relative to the image light.
Since the optical integrator having the beam splitter for splitting the light beam into a plurality of sub-beams is provided in the light-composite path, the light beam reversed relative to the image light is irradiated as a light beam having uniform illuminance distribution after being split into the sub-beams and superposed, so that the total light amount of the image light increases and high contrast ratio can be attained by irradiating the light beam again onto the reflective optical modulator.
In the present invention, the image information may preferably be transmitted to the reflective optical modulator by inputting an image signal corresponding to a color light to be modulated in a time-division manner, and a filter switch that switches color filters in synchronization with the image signal inputted to the reflective optical modulator may preferably be provided between the light source and the reflective optical modulator.
According to the above arrangement, by switching the light beam from the light source into red, green and blue light in synchronization with the image signal inputted to the reflective optical modulator using the color filter in a time-division manner, color projection image can be obtained with one reflective optical modulator.